Distribution of phosphoprotein p19 in rat brain during ontogeny: stage-specific expression in neurons and glia.

p19 is an evolutionarily highly conserved 19-kDa cytosolic protein that undergoes hormonally regulated phosphorylation in a variety of mammalian cells. Its expression is abundant in brain and testis and is developmentally regulated. Here we have used immunocytochemistry to define the cell types expressing p19 in the rat CNS during pre- and postnatal development. p19-like immunoreactivity appears in young postmitotic neurons in the mantle zone of the neural tube on embryonic day 12-13. Subsequently, it is abundant in most, if not all, early immature forms of both neurons and glia and declines to undetectable levels in fully differentiated cells. In adult brain, strong p19-like immunoreactivity remains detectable in selective regions, primarily where production of glia and neurons is known to persist, such as the subventricular zone of olfactory bulb and lateral ventricle, and the dentate gyrus. The abundance of p19 mRNA, determined by Northern blot analysis of selected brain regions, parallels the distribution of p19 assessed by immunocytochemistry, suggesting that control of p19 expression is pretranslational. Together with previous findings on the transient expression of p19 during spermatogenesis, the present data suggest that expression of p19 occurs in a number of cell lineages in a differentiation stage-dependent manner. In brain, p19 represents a new marker that may prove valuable for defining immature cell populations.